The newly discovered document — which the two have dated to the 1780s — was found in the town of Chichester archives, and is believed to have originally belonged to Duke of Richmond who was known as the “Radical Duke,’’ for the support he gave to Americans during the Revolutionary War, the researchers said.

The parchment was likely made in New York or Philadelphia. The researchers are still trying to determine the person who wrote the document and who paid for the foundational document of the United States to be copied.

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The signatories on the Sussex version of the document are not broken down by state, something that distinguished it from the Declaration in the National Archives, the researchers said.

In an academic paper, the researchers say the document probably was commissioned by James Wilson of Pennsylvania, who later helped draft the Constitution and was among the original justices appointed to the Supreme Court.

“The team hypothesizes that this detail supported efforts, made by Wilson and his allies during the Constitutional Convention and ratification process, to argue that the authority of the Declaration rested on a unitary national people, and not on a federation of states,’’ the researchers wrote in the statement.

The team, working with British officials, is working to carefully test the document in a way that will not damage the parchment.

According to the National Archives, the Massachusetts Historical Commission holds one of 26 copies of the Declaration of Independence prepared by John Dunlap, the printer for the Congressional Congress, after its signing on July 4, 1776.